Helicopter control linkage for automatic pitch and roll damping



Feb. 4, 1964 l. H. CULVER ETAL HELICOPTER CONTROL LINKAGE FOR AUTOMATICPITCH AND ROLL DAMPING Filed NOV, 30, 1960 3 Sheets-Sheet 1 FIG. I

IN V EN TORS IRVEN H. CULVER HENRY C. DANIELSON Agent Feb. 4, 1964CULVER ETAL 3,120,276

HELICOPTER CONTROL LINKAGE FOR AUTOMATIC PITCH AND ROLL DAMPING FiledNov. 50, 1960 3 Sheets-Sheet 2 FIG. 2

INVENTORS IRVEN H CULVER HENRY C. DANALELSON gnt Feb. 4, 1964 I. H.CULVER ETAL HELICOPTER CONTROL LINKAGE FOR AUTOMATIC PITCH AND ROLLDAMPING Filed NOV- 30, 1960 3 Sheets-Sheet 3 INVENTORS IRVEN H. CULVERHENRY C. DANIELSON United States Patent 3,12%),276 HELICOPTER CONTROLLINKAGE FOR AUTO- MATIC PITCH AND ROLL DAMPING Irven H. Culver, Burbank,and Henry C. Danielscn,

Northridge, Califi, assiguors to Lockheed Aircraft Corporation, Burbank,Calif.

Filed Nov. 30, 196i), Ser. No. 72,754) 3 Claims. (Cl. 170160.25)

This invention relates to a rotary wing aircraft and more particularlyto a control link-age therefor adapted to damp undesirable pitch androll oscillations.

A helicopter in flight is subject to disturbances from wind gusts orotherwise which displace the body of the helicopter with respect to therotor either in pitch or roll. As with all bodies in rotary motion, therotor tends to maintain its plane of rotation with any divergencebetween the rotor and the body of the helicopter being taken up inbending of the rotor blades and the rotor shaft. This divergence of thehelicopter body with respect to the rotor stores up a force causing itto spring back toward the rotor usually wit.1 such force that it passesthrough the neutral position from which it was disturbed in the oppositedirection rapidly increasing the oscillation until a dangerous conditionis approached.

The normal way to handle this oscillation problem is for the pilot tocontrol the plane of rotation of the rotor blades so that they aretilted in the direction of the pitch or roll of the helicopter body.Thus, there will be less of a building up of a spring force tendin toreturn the helicopter body to the attitude from which it was disturbed.Because there are many forces in and about the helicopter body duringits flight and on the ground which influence it about the pitch and rollaxes, the task of the pilot is great to maintain stabhity. Smalloscillations are liable not to be detected until they approach thedangerous stage.

One prior effort to solve this problem involved the use of an inertiadevice to sense vertical acceleration which then changed the cyclicpitch of the rotor blades so as to return the helicopters flight path tohorizontal. uch a device is shown in Patent No. 2,743,071 dated April24, 1956. Such device only corrected disturbances around the pitch axis.Correction was delayed vertical acceleration took place which normallyoccurred sometime after the disturbance.

it is the primary object of the present invention to provide in a rotarywing aircraft or the like, control linkage meaas operating automaticallyto damp the aforementioned disturbances about the roll and pitch axes.Relative movements between the rotor plane and the aircraft body causethe control linkage to alter the plane of rotation so as to minimize thedivergence.

It is another object of the present invention to provide a controllinkage means so connected that movement of the body of the helicopterwill cause the rotor to process in the direction of the movement so asto minimize storing of spring forces between the body and the rotorplane.

It is a further object of the present invention to provide a controllinkage which will sense and correct disturbances to the helicopter bodywith respect to the rotor immediately rather than at a later momen whenthe effects of such a disturbance are detected through a verticalacceleration device. The inertia sensing device detects disturbancesafter vertical acceleration has begun. Prior to that there is deflectionbetween the rotor and the body which results in the verticalacceleration. The present invention detects and corrects the earlierdeflection.

it is another object of the present invention to provide a controllinkage which will sense disturbances not only on a pitch axis but alsoroll axis and correct the same. Like rotor control linkage is providedon the roll axis and the pitch axis.

Further objects and advantages of the present invention will becomeapparent from a reading of the following specification taken inconjunction with the appended drawings.

FIGURE 1 shows the effects of disturbances to a rotary wing aircraftwith and without the present invention.

FIGURE 2 shows in perspective the control linkages accordin to thepresent invention.

FIGURE 3 is a side view of the pitch control linkage.

' IGURE 4 is a front view of the roll control linkage.

The operation of a conventional type rotary wing aircraft such as areinherently unstable and which therefore tend to fly in increasinglydivergent oscillating flight paths are indicated by curve 15 ofhelicopter 10 in FIG- URE 1. Curve "15 illustrates how the oscillationsdue disturbances of an inherently unstable helicopter aircraft tend toconstantly increase in velocity and amplitude. "vhere the rotary wingaircraft is of neutral stability, a disturbing gust of wind will causeit to follow a constant oscillatory path in of FIGURE 1. Thus, as shownin FIGURE 1, whenever the aircraft is disturbed by an oncoming gust orthe like as at point A on curve 16, the

rotor is tilted upwardly and the aircraft accelerated vertically to riseto a point indicated by B. The rotor, being a body in rotary motion,tends to maintain its plane of rotation in space much like a gyroscope.However, in all rotary wing aircraft there must be some elasticitybetween the rotor mast and the helicopter body. Thus, an upward gustwhich might pitch the body of the helicopter downward would cause adivergence between the horizontal plane of the body of the helicopterand the plane of the rotation of the rotor. These two planes will tendto spring together at crest B causing the rotor to be precesseddownwardly until it is pitched forward causing the path of the flight tobegin to descend as at point C in FIGURE 1. Opposite forces will beexperienced at the bottom of the next oscillation pitching thehelicopter upwardly again. The flight path then continues to oscillatewith a substantially constant velocity and amplitudes above and belowthe horizon of the original straight line flight path. On the otherhand, as illustrated by the curve 7, whenever a rotary wing aircraftembodying the present invention is met by an oncoming gust and pitchesupwardly, the control linkage goes into operation automatically such asat the position indicated at A whereby to antticipate and dampen theforces normally producing phugoidal oscillation.

FIGURE 2. is a perspective of the helicopter with the control linkagewhich goes to make up the present invention. The helicopter is shownequipped with the conventional control stick 2% which, when moved fromside to side, provides roll input forces to the rotor and when movedfore and aft provides pitch input forces. The control forces throughcontrol stick 20 are transmitted through a push-pull rod 22 and a torquetube 23 to the pitch and roll linkages for the rotor.

Pitch control forces are transmitted through rod 22. Torque tubes 23 hasupstanding plates 27 on its forward end with a pin 28 at its upper endaround which the stick 26 is pivoted in its fore and aft motion. Thelower edge of the stock 21' is pivoted to the push rod 22. Push rod 22is pivoted to the lower arm of bell crank 31 which is pivoted to thehelicopters body structure so that fore and aft forces of push rod 22will cause push rod 32 to move up and down. Push rod 32 is pivoted tothe forward arm of bell crank 34 which is pivoted to the helicopterstructure. The lower arm of bell crank 34 is pivoted to push rod 36which is pivoted at its aft end to 3 bell crank 38 again pivoted to thehelicopter body. The aft arm of bell crank 38 is'pivoted at 39 to pushrod 40 which in turn is pivoted to the swash plate 42.

Roll control forces are transmitted through the torque tube 23 and itslateral arm 46. Lateral movements of the stick 20 cause the torque tube23 to move lateral arm 46 causing the push rod 48 to move up or down.The upper end of push rod 48 is pivoted to hell crank 50 which ispivoted to the helicopter body structure on a fore and aft axis. Thelower arm of hell crank 50 is pivoted to push rod 51 which is in turnpivoted in turn to the lower arm of bell crank 53 again pivoted to thehelicopter structure. Movement of bell crank 53 around its pivot willcause the push rod 55 to tilt the swash plate 42 around a lateral axisfor roll input forces.

It should be noted at this point that the swash plate 42 as shown isthat described with more particularity in copending U.S. patentapplication Serial Number 844,886 to a Helicopter dated October 7, 1959,now Patent 3,080,001. In that application as in the showing in FIG- URE2, input forces are transmitted by means of springs from the swash plateto the rotor blades necessitating input forces 90 prior to the time ofthe desired change according to the well-known law of gryoscopicprecession. Thus, input forces to the rotor for pitch control will beapplied on the lateral axis or side of the swash plate and roll controlforces will be applied on the longitudinal axis of the craft in eachcase 90 before the desired result. If the linkage system according tothe present invention is to be used on a helicopter having positivepitch control inputs to the rotor blades such as shown in the U.S.Patent No. 2,743,071 dated April 24, 1956, the pitch control forces willbe applied around the lateral axis and the roll control forces aroundthe longitudinal axis of the swash plate as shown in FIGURE 1 of thatpatent. Thus, push rods 40 and 55 of FIGURE 2 of this application wouldbe connected to the swash plate 42, 90 to the counterclockwise form thatshown assuming that the rotor rotated counterclockwise as viewed fromabove.

The pitch control linkage is shown in a side view in FIGURE 3. To reviewagain the motion of the control linkage it will be remembered that foreand aft movement of stick 20 will cause it to pivot around the pin 28causing rod 22 to move bell crank 31 which will cause the push rod 32 tomove up and down moving bell crank 34 about its pivot causing push rod36 to move fore and aft and bell crank'38 to rotate about its axis. Bellcrank 38 is pivoted at point 39 to push rod 40 which is attached to theswash plate 42 at its upper end. Note'at this point that the pivot point39 is aft of a lateral plane passing through the center of rotation ofthe rotor shaft 60 in the direction of rotation of the rotor. The rotorshaft 60 is driven by engine 61 connected'to gear box 63 through shaft64 and universal joint 65. Gear box 63 is mounted in frame work 66 whichis attached at four points by shock mounts 68 to the helicopter body.Shock mounts 68 permit a small amount of motion of the gear box frame 66with respect to the helicopter body to which the shock mounts 68 areattached. Any disturbances be tween the rotor and the helicopter bodywill be reflected substantially in rotation of the body about theeffective center of rotation 70 defined as the intersection of thelongitudinal axis of the drive shaft and a horizontal plane passingthrough the center of the shock mounts 68. Shock mounts 68 will permitthis rotaiton of the body by extension on one side and compression onthe other.

For purposes of understanding, the rotor may be considered to maintainits plane of rotation with the body doing all of the movement. Shouldthere be a disturbance which will cause the body of the helicopter to bepitched downwradly with respect to the plane of rotation of the rotor,there will be a counterclockwise rotation of the helicopter body aboutthe effective center of rotation 74). Recall again that the pivot point39 between the bell crank 38 and the push rod 40 to the swash plate 42is 4- displaced slightly aft of the lateral plane passing through thecenter of rotation of the shaft 60 in the direction of its rotationwhich means it is slightly aft of the effective center of rotation 70.Thus, counterclockwise rotation of the helicopter body about center ofrotation 70 will cause pivot point 39 to move upwardly with respect toits original position, and the rod 40 will push up on swash plate 42.This up movement on swash plate 42 will cause the rotor to precess sothat its highest point of rotation then will be on the aft edge of therotation disc considering that input forces to a rotating body areeffective 90 later in the plane of rotation. Thus, there will be lessangular divergence between the plane of rotation and the I longitudinalaxis of the helicopter body because the rotor to the right.

is caused to precess in the direction in which the helicopter body haspitched. This minimizes the build up FIGURE 4 shows the roll controllinkages looking.

from the front of the aircraft. Reviewing the normal control inputs wefind that if a starboard or right roll is desired the control stick willbe moved to the right (left as viewed in FIGURE 4). This will rotate thearm 46 counterclockwise pulling the rod 48 down. Rod 48 in turn rotatesbell crank 50 counterclockwise moving the rod 51 This in turn rotatesthe bell crank 53 counterclockwise moving the rod 55 up tilting theswash plate around lateral axis toward the back of the helicopter. Sinceany control inputs to the rotary body are effective after the input, therotor disc reacts to the control input when it reaches a point 90 laterin its totation or the left side of the disc will be tilted up as viewedfrom above if the rotation of the rotor is counterclockwise looking fromabove. By similar reasoning a movement of the control stick 20 to theright in FIG- URE 4 which would produce a left roll would pull rod 55downwardly thus tilting the rotor disc down to the left or the port sideof the helicopter creating a left roll.

Note that the pivot point 54 between bell crank 53 and push rod 55 isoffset to one side of a vertical plane passing through the rotationalaxis of the rotor and the longitudinal axisof the body :10 in thedirection of rotation of the rotor disc so that should there be amovement of the helicopter body =10 about the effective center ofrotation 70, rod 55 will be effectively moved up or down thus changingthe plane of rotation of the rotor so'that it precesses in the directionof the disturbance of the body.

Thus looking at FIGURE 4 should the body rotate in a counterclockwisedirection with respect to the rotor plane of rotation the pivot 54 beinglocated to the right of the effective center of rotation 70 will causerod 55 to move upwardly to apply an up force on the forward edge of theswash plate causing the plane of rotation of the rotor to tilt upwardly90 later or on the left side of the aircraft (or the right side asviewed in FIGURE '4). Thus the rotor follows the disturbance applied tothe aircraft body. Conversely, should the aircraft body rotate clockwiseas viewed in FIGURE -4 the pivot point 54 will be moved down withrespect :to the center of rotation 70 pulling rod .55 down thus causingthe plane of rotation to tilt clockwise as seen in FIGURE 4 followingthe in-' adventent roll of the body so as to neutralize the storing upof spring forces between the rotor and the body to minimize spring back.

The location of the pivot point 39 to one side of the vertical planepassing laterally through the shaft 60 and pivot point 54 to one side ofthe vertical plane passing longitudinally with respect to the bodythrough rotorv shaft 60 in the direction of rotor rotation mightconceivably be at the lower side of the helicopter body instead or"close to the center of rotation 79. That is, the push rod 49 could beextended downwardly to meet bell crank 31 which would be located more orless aft and under the center of rotation so that two push rods 22 and40 and a single bell crank 31 would be the total linkage required forpitch control. Likewise, the push rod 55 could be e ended to meet withthe arm 46 on the torque tube 23 which would be elongated in such amanner so that pivot point 54 would be located to one side of thevertical plane passing through to the longitudinal axis of thehelicopter and shaft 641. In both instances, divergence of thehorizontal plane of the helicopter body and the plane of rotation of thehelicopter rotor will cause the push rods 46 and 55 to effectivelylengthen or shorten so as to cause the rotor to precess in the directionof the pitch or roll of the helicopter body to dampen disturbances toit.

As indicated in a previous paragraph the present invention is notrestricted to the particular swash plate rotor combination describedherein but may be used on helicopters embodying a positive pitch controlto the rotor blades wherein the control inputs are connected directly tothe feather axis of each rotor blade rather than through a springattached to the swash plate.

We claim:

1. In a helicopter having a body, a rotor drive shaft elasticallymounted with respect to the body, a rotor attached to the drive shdt,and a swashplate mounted on said drive shaft below said rotor, a rotorcontrol mech anism comprising: a generally upright link having a pivotalconnection to the swashplate and to the body, said swashplate connectionand the longitudinal axis of the drive shaft defining a reference plane,said body connection being oustide and ahead of said plane as determinedby the direction of rotor rotation, whereby the link exerts a force onthe swashplate when the body is displaced with respect to the rotor,which force causes the rotor to precess in the same direction as thebody displacement and thereby automatically damps relative displacementof the rotor and body.

2. In a helicopter having a body, a rotor drive shaft elasticallymounted with respect to the body, a rotor attached to the drive shaftand adapted for counterclockwise rotation, and a swashplate mounted onsaid drive shaft below said rotor; a pitch control mechanism comprising:linkage means for tilting said swashplate and thereby supplying acontrol input to the rotor, said means including a generally uprightlink having a pivotal connection with the swashplate and with theremainder of said said means, said swashplate connection lying in avertical reference plane passing laterally through the longitudinal axisof the drive shaft, said connection to the remainder of the linkagemeans lying aftward of said plane, whereby said link exerts a generallyupward force on the swashplate when the body is displaced nose-down withrespect to the rotor and a generally downward force on the swashplatewhen the body is displaced nose-up with respect to the rotor, whichforces causing the rotor to precess in the same direction as the bodydisplacement and thereby automatically damping relative pitchdisplacement of the rotor and body.

3. In a helicopter having a body, a rotor drive shaft elasticallymounted with respect to the body, a rotor attached to the drive shaftand adapted for counterclockwise rotation, and a swashplate mounted onsaid drive shaft below said rotor; a roll control mechanism comprising:linkage means for tilting said swashplate and thereby supplying acontrol input to the rotor, said means including a generally uprightlink having a pivotal connection with the swashplate and with theremainder of said leans, said swashplate connection lying in a verticalreference plane passing longitudinally through the longitudinal axis ofthe drive shatt, said connection to the remainder of the linkage meanslying to the left of said plane, whereby said link exerts a generallydownward force on the swashplate when the body is displaced laterally tothe left and a generally upward force on the swashplate when the body isdisplaced laterally to the right, which forces causing the rotor toprecess in the sarne direction as the body displacement and therebyautomatically damping relative roll displacement of the rotor and 'body.

References Cited in the file of this patent UNITED STATES PATENTS2,517,509 Sikorsky Aug. 1, 1950 2,519,762 Hoffman Aug. 22, 19502,569,061 Hunt Sept. 25, 1951 2,720,271 Alex Oct. 11, 1955 2,735,500Perry Feb. 21, 1956 2,743,071 Kelley Apr. 24, 1956 2,792,189 Altemus May14, 1957 2,949,254 Bauer Aug. 16, 1960 2,959,230 Doman Nov. 8, 1960

1. IN A HELICOPTER HAVING A BODY, A ROTOR DRIVE SHAFT ELASTICALLYMOUNTED WITH RESPECT TO THE BODY, A ROTOR ATTACHED TO THE DRIVE SHAFT,AND A SWASHPLATE MOUNTED ON SAID DRIVE SHAFT BELOW SAID ROTOR, A ROTORCONTROL MECHANISM COMPRISING: A GENERALLY UPRIGHT LINK HAVING A PIVOTALCONNECTION TO THE SWASHPLATE AND TO THE BODY, SAID SWASHPLATE CONNECTIONAND THE LONGITUDINAL AXIS OF THE DRIVE SHAFT DEFINING A REFERENCE PLANE,SAID BODY CONNECTION BEING OUTSIDE AND AHEAD OF SAID PLANE AS DETERMINEDBY THE DIRECTION OF ROTOR ROTATION, WHEREBY THE LINK EXERTS A FORCE ONTHE SWASHPLATE WHEN THE BODY IS DISPLACED WITH RESPECT TO THE ROTOR,WHICH FORCE CAUSES THE ROTOR TO PRECESS IN THE SAME DIRECTION AS THEBODY DISPLACEMENT AND THEREBY AUTOMATICALLY DAMPS RELATIVE DISPLACEMENTOF THE ROTOR AND BODY.